MOB-399: slim builds never strip an OTP lib the app needs

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Fixes MOB-399.

mix mob.release --android (default slim) stripped inets from the bundled OTP tree regardless of the app. Operator's release then logged plugin :mob_ash: OTP application failed to start ... {:inets, {~c"no such file or directory", ~c"inets.app"}} (ash → igniter → inets). Debug deploys ship the full tree, so only release broke.

Rule: a slim pass never strips an OTP lib any shipped app lists in its .app applications/included_applications, transitively.

• MobDev.OtpRequiredApps: closure of MobDev.HotPush.runtime_lib_names/0 through the bundled OTP tree's lib/*/ebin/*.app.
• Android release: OtpAssetBundle.build/3 takes :required_apps (precedence: defaults − required + :strip_extra_prefixes − :keep_prefixes), returns :kept_required, which mix mob.release logs.
• iOS release script: skips names in MOB_SLIM_KEEP_LIBS (set by Release.build_ipa/1).
• mix mob.deploy --slim: OtpAudit.Slim.compute_strip_set/1 takes :required_libs (after baseline/audit, before :drop_libs/:keep_libs).
• HotPush's _build traversal follows included_applications too (shared .app reader).

Tests: otp_asset_bundle_test (transitive + included_applications kept, unrelated libs still stripped), slim_test (:required_libs precedence).

Proof on Operator: see the comment below (slim release AAB → universal APK on an emulator).

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Proof on Operator (scratch clone of ~/code/operator at 849a7a7, mob_dev via path to this branch):

mix mob.release --android (default slim):

kept OTP libs the app needs (not slimmed): inets
5929 files, 306MB → 55MB
AAB: .../android/app/build/outputs/bundle/release/app-release.aab

otp.zip contains lib/inets-9.7/ebin/inets.app. Universal APK via bundletool build-apks --mode=universal (release keystore): 125,901,777 bytes. Installed on emulator-5562 (sdk_gphone64_arm64), cold launch, logcat:

I Elixir  : [mob] plugin :mob_ash: OTP application started
I Elixir  : [dyn] boot: %{status: :proven, mode: :normal, ...}

24 plugin OTP apps started; 0 failed to start lines (before: plugin :mob_ash: OTP application failed to start ... {:inets, {~c"no such file or directory", ~c"inets.app"}}). The repeated erl_prim_loader ... eacces. Target: .. Function: list_dir lines are pre-existing noise also seen on debug deploys (on-device compiler code path), unrelated to slimming.

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Review: reviewer subagent (Codex rate-limited until 2026-10-09 21:14): MERGE. No blocking or should-fix findings; nitpicks: no test of the HotPush included_applications traversal end to end; iOS keep set uses Mix.Project.build_path while the script ships _build/dev (pre-existing).